The present invention relates to a battery system having a battery which is designed to supply a high-voltage network and can be connected by at least one of its high-voltage network terminals via a contactor. The invention also relates to a method for switching a contactor for a battery which is designed to supply a high-voltage network and can be connected by one of its high-voltage network terminals via the contactor. The invention also relates to a vehicle having a battery system just mentioned.
Battery systems having batteries which can each supply a high-voltage network with a high voltage are used in vehicles (automobiles). Therefore, the battery cells or battery modules of such batteries are usually connected in series. Such batteries must then provide only small currents even in the case of high powers. In this case, the batteries are connected by their high-voltage terminals, that is to say the terminals via which the battery delivers the high voltage to the high-voltage network, via traction lines. Contactors are usually used in the traction lines both at the positive and at the negative high-voltage terminal of the battery. The contactors can be used to disconnect such a battery from the high-voltage network or from the remaining high-voltage system of the vehicle during parking or in a defective functional state (fault).
Such a contactor 10 is illustrated in FIGS. 1 to 3. In this case, the same reference symbols are used for the same components.
FIG. 1 illustrates a closed contactor 10 and FIG. 2 illustrates an open contactor 10. The contactor 10 is in the form of a magnetic switch 11 having a control coil 20. In this case, the magnetic switch 11 comprises a movable contact bridge 30 and two terminals 40. The contactor 10 closes in a state in which a control current flows through the control coil 20 and opens in a further state in which no current flows through the control coil 20.
If a control current flows through the control coil 20, the contact bridge 30 is moved toward the terminals 40 by means of magnetic force and is pressed against these terminals 40. If no current flows through the control coil 20, the contact bridge 30 immediately returns to its position at a distance from the terminals 40.
In order to generate the control current, the control coil 20 must be supplied with electrical energy. For this purpose, the contactor 10 can be connected to a supply unit (energy source) 50, for example via a control device 60 which is preferably a battery control device.
In this case, the supply unit 50 may be the low-voltage network (vehicle electrical system) of a vehicle which provides a voltage of 12 V. If the control coil 20 is connected to the supply unit 50 by means of the control device 60, the control current flows through the control coil 20 and the contactor 10 closes. If the connection between the control coil 20 and the energy source 50 is interrupted by the control device 60, no current flows through the control coil 20 and the contactor 10 opens.
Such contactors 10 used in the traction lines of a battery can disconnect currents of approximately 1 to 2 kA in a defective functional state. Fuses (fusible links) are usually used for higher currents.
As illustrated in FIG. 3, for currents of more than 3 to 10 kA, the result is a repulsion between the terminals 40 and the contact bridge 30 caused by the Lorentz force 70 occurring in a closed contactor 10. Currents of more than 3 to 10 kA may occur, for example, when there is a short circuit in the traction lines of the battery or when there is a short circuit in an inverter electrically coupled to the battery. This phenomenon is referred to as levitation. In this case, despite an active control coil 20 through which the control current flows, a small distance is produced between the terminals 40 and the contact bridge 30. Arcs 71 which fuse the contact surfaces of the terminals 40 are formed via this air gap. If the short-circuit current is then interrupted by the fuse connected to the corresponding high-voltage terminal, the contact bridge 30 presses the two fused terminals 40 together. In this case, the material solidifies and the contact bridge 30 can no longer be opened after switching off the control current flowing through the control coil 20. This fault is referred to as contactor adhesive. The two terminals 40 of the contactor 10 are connected to one another in a conductive manner and cannot be disconnected.
The time during which the contactor 10 must be able to carry the short-circuit current without suffering this effect is always longer than the time needed by the associated fuse (fusible link) to disconnect this short-circuit current in a contactor 10 with ideal dimensions. If a contactor 10 is dimensioned in this manner, the contactor 10 does not fuse on account of this effect, can still be switched after the short-circuit current has been disconnected by the tripped fuse and can disconnect the battery from the high-voltage network of the vehicle.
Such contactors 10 are usually opened and closed by the battery control device of a battery in which the contactors 10 are used. In this case, the battery control device can forward the low voltage of 12 V provided by the low-voltage network of a vehicle to the contactors 10.
If this low voltage of 12 V fails, the contactors 10 immediately open. There is the risk of the contactors 10 opening in an undesired manner even in the case of voltage fluctuations in the low-voltage network of the vehicle.
The document DE 199 47 105 C2 discloses a switching contactor having a magnetic drive and quick disconnection implemented using circuitry. As a result of the quick disconnection, the switching contactor can be permanently opened if there is a short-circuit current flowing through the switching contactor in order to be protected against contact fusing.